The invention relates to a method for setting a predetermined travel of an actuator, in particular a piezo-electric actuator for an injector of an injection system, and an actuator regulation device for the implementation of such a method.
In injection systems in internal combustion engines fuel is injected into the combustion chambers of the internal combustion engine by means of injectors, with the injection process being regulated by piezo-electric actuators, which either release or close a nozzle opening on the basis of their electric regulation. For correct operation of the injector the piezo-electric actuator must therefore achieve constant travel. For the purposes of setting the predetermined actuator travel in various patent applications, such as for example DE 197 23 932, DE 196 52 809 and DE 196 52 801, the physical knowledge is exploited that actuator travel essentially behaves in proportion to the electrical energy supplied. During regulation of the actuator therefore the electrical charge supplied and the resulting electrical voltage are measured, so that they can be used to calculate the electrical energy supplied.
One disadvantage of the known actuator regulation device described above is the fact that the functional relationship between the electrical energy supplied to the actuator and the resulting actuator travel is temperature-dependent, which when used in a car results in discrepancies between the actuator travel and the predetermined target value due to the large temperature fluctuations occurring during operation.
The object of the invention is therefore to improve the known actuator regulation described above so that the actuator travel can be set irrespective of temperature.
The object can be achieved, by a method for setting a predetermined travel of an actuator, in particular a piezo-electric actuator for an injector of an injection system, in which a first electric state variable of the actuator is set, which determines the travel of the actuator, wherein the first electric state variable is set in accordance with the temperature of the actuator to avoid temperature-induced fluctuations of the actuator travel.
The temperature of the actuator is measured and the first electric state variable can be set in accordance with the measured value for temperature of the actuator. The temperature of the cooling water, the engine oil, and/or the fuel is measured and the temperature of the actuator can be derived from one or more of these measured temperature values. A second electric state variable of the actuator is measured and a target value can be determined from the measured value of the temperature of the actuator for the second electric state variable of the actuator, with the measured value of the second electric state variable being compared with the target value of the second electric state variable, to verify the correctness of the temperature measurement or the electric state variables. A second electric state variable of the actuator is measured and a reference variable can be calculated from the first electric state variable and the second electric state variable, which corresponds to a predetermined travel of the actuator irrespective of the temperature of the actuator, with the first electric state variable being regulated in accordance with the reference variable. The first electric state variable can be the electrical charge of the actuator. The second electric state variable of the actuator can be the electrical voltage of the actuator.
The object can also be achieved by a method for setting a predetermined travel of an actuator comprising the steps of:
setting a first electric state variable of the actuator, which determines the travel of the actuator, in accordance with the temperature of the actuator to avoid temperature-induced fluctuations of the actuator travel,
measuring a second electric state variable of the actuator,
calculating a reference variable from the first electric state variable and the second electric state variable, which corresponds to a predetermined travel of the actuator irrespective of the temperature of the actuator,
regulating the first electric state variable in accordance with the reference variable, wherein the reference variable is calculated on the basis of a known temperature-dependent characteristic curve for the first electric state variable and a known temperature-dependent characteristic curve for the second electric state variable, so that both the first electric state variable and the second electric state variable behave according to the predetermined characteristic curves.
The first electric state variable can be the electrical charge of the actuator. The second electric state variable of the actuator can be the electrical voltage of the actuator. The actuator can be a piezo-electric actuator for an injector of an injection system.
The object can furthermore ba achieved by an actuator regulation device, in particular for regulating a piezo-electric actuator of an injection system for an internal combustion engine, comprising a drive circuit for setting a first electric state variable of the actuator, with the first electric state variable determining the travel of the actuator, and a control or regulation unit for setting the first electric state variable in accordance with the temperature of the actuator.
At least one temperature sensor can be provided to determine the temperature of the actuator, with a first characteristic curve member being positioned between the control or regulation unit and the temperature sensor to determine a target value for the first electric state variable in accordance with the temperature of the actuator. A number of temperature sensors can be provided to determine the oil temperature, the cooling water temperature and/or the fuel temperature, with the temperature sensors being connected on the output side to an analysis unit, which determines the temperature of the actuator from the oil temperature, the cooling water temperature and/or the fuel temperature. An electrical measuring device can be provided to measure a second electric state variable of the actuator and the temperature sensor can be connected to a second characteristic curve member, which determines a target value for the second electric state variable from the measured value of actuator temperature, with the second characteristic curve member and the electrical measuring device being connected to a comparison unit, which compares the target value of the second electric state variable with the measured value of the second electric state variable, in order to verify the correctness of the temperature measurement. An electrical measuring device can be provided to measure a second electric state variable of the actuator and this is connected on the output side to a computing unit, which calculates a reference variable for a regulation unit from the first electric state variable and the second electric state variable, with the regulation unit regulating the first electric state variable in accordance with the reference variable. The first electric state variable can be the electrical charge of the actuator. The second electric state variable of the actuator can be the electrical voltage of the actuator.
The object can also be achieved by an actuator regulation device comprising a drive circuit for setting a first electric state variable of the actuator, wherein the first electric state variable determines the travel of the actuator, a control or regulation unit for setting the first electric state variable in accordance with the temperature of the actuator, an electrical measuring device being provided to measure a second electric state variable of the actuator, and a computing unit connected to the electrical measuring device on the output side, which calculates a reference variable for a regulation unit from the first electric state variable and the second electric state variable, wherein the regulation unit regulates the first electric state variable in accordance with the reference variable, and wherein the computing unit calculates the reference variable on the basis of a known temperature-dependent characteristic curve for the first electric state variable and a known temperature-dependent characteristic curve for the second status variable, so that both the first electric state variable and the second electric state variable behave according to the predetermined characteristic curves.
The first electric state variable can be the electrical charge of the actuator. The second electric state variable of the actuator can be the electrical voltage of the actuator. The actuator can be a piezo-electric actuator of an injection system for an internal combustion engine.
The invention embraces the general technical doctrine of taking actuator temperature into account during electrical regulation of the actuator, in order to avoid temperature-induced fluctuations of the actuator travel.
In a variant of the invention the actuator temperature is measured for this purpose so that it can be taken into account for electrical regulation of the actuator. The actuator temperature is preferably not measured directly here but indirectly, with temperature sensors detecting the oil temperature, the fuel temperature and/or the water temperature, to derive the actuator temperature from these. However other state variables can be detected in addition to the state variables mentioned above, to determine the actuator temperature. The actuator temperature is preferably calculated from a combination of measurement variables, in order to compensate for measurement errors. Actuator temperature is preferably determined in the stationary engine state so that all temperature sensors supply approximately the same measured value.
Instead of the indirect measurement of actuator temperature described above, the actuator temperature can however also be measured directly, for example by positioning a temperature sensor on the actuator. Instead of this the actuator temperature can also be determined by measuring the temperature-dependent capacity of the actuator, by then comparing the measured value of the capacity with the known and previously measured temperature-dependent characteristic curve for capacity of the actuator.
With temperature-dependent electrical control of the actuator a known temperature-dependent characteristic curve is preferably taken as the basis and this shows the electrical charge to be supplied to the actuator to achieve constant travel. The necessary electrical charge is then determined according to this characteristic curve from the measured actuator temperature and the actuator is regulated accordingly. In this manner it is advantageously ensured that actuator travel is constant irrespective of actuator temperature.
In an advantageous embodiment of this variant of the invention the electrical voltage of the actuator is also measured to verify the correctness of the temperature measurement. In addition to the measured value of the electrical voltage of the actuator, a theoretical value is also calculated for the electrical voltage of the actuator, which results from the measured actuator temperature on the basis of a predetermined actuator-specific, temperature-dependent characteristic curve for voltage. In the case of a correct temperature measurement the measured value for actuator voltage must be essentially equal to the theoretically calculated voltage value, resulting from actuator temperature and the characteristic curve for voltage for the actuator. In the event of a discrepancy between the measured voltage value and the theoretically calculated voltage value, there is assumed to be an error. With this embodiment therefore actuator temperature is first measured or derived from one or more measured values. In the case of the measured actuator temperature, the electrical variables charge and voltage of the actuator are determined, in order then to track the actuator charge used as the regulation variable, so that actuator travel is constant. Charge and voltage of the actuator are then also measured, in order to determine the actuator temperature from these and to compare it with the measured value for actuator temperature.
In a different variant of the invention the temperature of the actuator is taken into account for its electrical regulation without requiring a temperature sensor. Two known and previously measured actuator-specific characteristic curves are used as a basis for this. One characteristic curvexe2x80x94as already stated abovexe2x80x94shows the electrical charge to be applied to the actuator to achieve a predetermined travel as a function of temperature. The other characteristic curve on the other hand shows the electrical voltage of the actuator required to achieve a predetermined travel as a function of temperature. To achieve a predetermined travel, both voltage and charge should therefore behave according to the predetermined characteristic curves, so that a temperature-independent reference variable can be calculated from voltage and charge and used to regulate the electrical charge to be applied to the actuator. The actuator charge is preferably regulated in such a way that the temperature-independent reference variable assumes a constant value. This variant of the invention has the particular advantage that a separate temperature sensor is not required.